This invention relates to television measuring apparatus and more particularly to apparatus employing digital techniques for measuring time intervals associated with a television signal.
As is well known, television standards are criteria which dictate the characteristics to be employed in a television system. The standards assure that the component parts of the system are designed and operated on a common basis to optimize performance available in regard to a particular system.
Essentially, the timing intervals associated with the television signal are sometimes referred to as scanning standards and synchronization standards. The manner in which a television scene is explored or processed for its luminance and chrominance value is defined by the scanning standards.
To coordinate the scanning and color modulation processes of transmitters and receivers, four forms of sychronization signals are employed. Generically, these can be referred to as (1) vertical sync signals, (2) equalizing sync signals, (3) horizontal sync signals, and (4) color sync signals. The first three of these are collectively known as the deflection sync signals. The function of these signals is to initiate the vertical and horizontal retrace motions in scanning deflection. These signals are common and are employed in both color and monochrome transmissions.
The color sync signal which is employed in a color transmission constitutes the phase reference employed in the modulation of the chrominance subcarrier. In the composite television signal, the deflection sync signals occupy the portion of the modulation envelope adjacent to the blanking level and separate from the picture information region. The color sync signal is centered on the blanking level and extends in part into the picture information region. It is customary, for example, to specify the synchronization signals in diagrammatic form and many texts show the complete nature of the signal in such form. Reference is made, for example, to a text entitled "Electronic Engineers Handbook" by Donald G. Fink, a McGraw-Hill publication (1975), Chapter 20 which has representations of such diagrams clearly showing the synchronization signals briefly described above.
Based on present F.C.C. transmission specifications and based on Governmental requirements imposed upon the broadcasting facilities, it is necessary to monitor such intervals and to assure that the television signal as transmitted corresponds to the governing agency's requirements. The measurement of such intervals has been accomplished in the prior art by employing various types of equipment generally designated as wave form monitors or wave form analyzers. These devices basically employ a special type of oscilliscope, since the average oscilliscope does not incorporate the necessary refinements that are required for such examinations.
Essentially, a wave form monitor can be locked to a particular field and line that is of interest and such devices have means for expanding the display to the degree necessary to observe the slope of the leading or trailing edges of special pulses. Such monitors generally employ a wide band deflection amplifier, a driven type sweep circuit, a special type of sychronizing system which may include a calibrated sychronization delay circuit, a precision sweep calibrator and a high voltage cathode ray tube. The prior art devices as described above enable one to view the television signal on the face of an oscilliscope and based on the sweep rate and so on, the user or technician can make visual determinations and calculations in order to assure that the timing intervals are within the necessary specifications. As one can ascertain, these techniques require skill in that careful interpretation and observation are required.
It is an object of the present invention to perform the measurement of timing intervals automatically and to display in digital form, the value indicative of the interval selected. The apparatus allows the automatic logging and remote monitoring of timing measurements as would be required in studios, transmission networks and at unattended transmitter operations.
The apparatus to be described employs digital processing techniques to enable one to select a parameter, to be measured, by means of a pushbutton or selectively activated switch associated with that function and located on the front panel of the interval timer. In this manner, a user can select any one of a plurality of timing intervals associated with the television signal and obtain a direct digital readout of the interval.
As should be apparent, the television interval timer to be described substantially reduces the amount of time and effort required to make such measurements to thereby enable a television broadcaster to maintain the specifications required by the particular governmental agency.